Cathode ray tube



May 18, 1937. M. VON ARDENNE CATHODE RAY TUBE Filed May 24, 1934INVENTOR NHNFRED VUN HRDENNE BY %w/% ATTORNEY 2 Pi .Ea E9: (9 Q m -1 FlE1 1-: 53.;

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8 43 a BT50 Patented May 18, 1937 PATENT QFFICE 2,080,449 cA'rHooE anyTUBE Manfred von Ardenne, Berlin, Germany, assignor, by mesneassignment-a to Radio Corporation of America, a corporation of DelawareApplication May 24, 1934, Serial No. 727,206

In Germany June 12, 1933 12 Claims.

My invention relates to improvements in and methods of operation ofcathode ray tubes, in particular for use as oscillographs and in cathoderay television systems. The general form of 5 cathode ray tubesheretoforeknown in the art used, for oscillographs or in cathode raytelevision comprises the three essential parts: a

thin beam or pencil of electrons, a fluorescent...

target or luminous screen for the electron 10 pencil to strike againstto produce a recording high spot, and a mechanism for deflecting theelectron beam and varying the intensity of the luminous spot on thescreen for producing an image or pattern of desired configuration and l5characteristics.

In the ordinary cathode ray tubesas known in the art used foroscillographic and television purposes, deflecting potentials of severalhundred volts are necessary to move the electron beam 20 over the entiresurface of the fluorescent screen. This low sensitivity of deflectionnecessitates the use of very high anode voltages and high amplificationin the sweep or control circuits for produring the deflectingpotentials.

25 It is a main object of my invention to provide a novel method of andmeans for deflecting the electron beam in a cathode ray tube which ischaracterized by considerably increased sensitivity of the deflectionwhile enabling the use of 30 very high electron velocities required forinsuring a brilliant luminous spot upon the fluorescent screen producedby the impact of the electron ray.

As is well known, the sensitivity of deflection 35 of an electron raymay be increased if the deflection takes place at a place where theelectrons travel at low speed. In recognition of this fact it hasalready been attempted to construct tubes in which the electron beam isinitially accelerated to a fraction only of the desired final speed andis then passed. through the deflecting system whereupon a finalacceleration is applied to secure sufficient kinetic energy of theelectron beam striking the fluorescent surface to produce a 45 brightluminous spot' thereon. By this scheme the further advantage is obtainedespecially in tubes containing a gaseous atmosphere that on account ofthe low velocity in the ray producing system, the destruction of thecathode by gaseous 50 ions is limited to a minimum. I

However, it has not been possible in practice to satisfactorily carryout the aforementioned scheme for the following reasons among others.

It was not possible to apply an additional or 55 final acceleration toan electron pencilsubjected to a large deflection in both coordinatedirections, without'causing serious interference with the properoperation of the tube.

Accordingly it is a further object of my invention to provide a means inthe path of a concentrated electron ray for additionally accelerating ordecelerating the electrons substantially independent of the directionand/or degree of deflection of the electron pencil relative to a normalor zero position and without any additional impairment of the properfunctioning of the tubes. 7

It was furthermore found especially in the case of gas filled cathoderay tubes, that the electron speed in the ray-producing and reflecting 5space had to be of comparatively high value (several hundred volts) inorder to secure a sufficient current intensity at the top of the ray orin turn a sufficiently brilliant luminous spot on thefiuorescent screen.

Accordingly, a further object of my invention consists in a novel methodand means whereby an extremely low electron speed may be employed withinthe space of the deflecting system, resulting in aconsiderably increasedsensitivity of reflection while maintaining simultaneously high velocityof the electron ray at the place where the ray strikes against thefluorescent screen.

Still a further object of my invention is the 30 provision of a novelelectrode construction in a cathode ray tube for deflecting the beam ata place immediately near the cathode where the electrons move with thelowest velocity, resulting in greatly increased sensitivity of thedeflection.

One of the difficulties experienced with cathode ray tubes as knownheretofore in the art is the fact that a substantial reaction,especially capacitative reaction, may take place between the 40deflecting systems used for deflecting the beam in both a vertical andhorizontal direction, in particular if two pairs of capacitativedeflecting plates are used. This deflection may result in substantialdecrease of the sensitvity of deflection, in distortion, and otherwisegreatly interfere with the proper operation of the tube.

Accordingly it is a further object of my invention to provide efficientscreening means between the deflecting systems in a cathode ray tube forsubstantially eliminating interaction between deflecting systems.

These as well as further objects and aspects of my invention will bebetter understood by reference to the following detailed descriptiontaken together with the accompanying drawing wherein I have shownseveral cathode ray tube constructions embodying my invention. Theembodiments shown are to be taken as being illustrative only of theunderlying principle and novel features of the invention which, as willbecome obvious, is subject to various modifications and variationscoming within the broadest scope thereof as expressed in the appendedclaims.

In the drawing; in which similar reference nu-' merals identify similarparts in the different views;

Figure 1 illustrates an electrode .construction for accelerating ordecelerating an electron beam in accordance with my invention;

Figure 2 schematically illustrates a cathode ray tube having anelectrode according to Figure 1 embodied therein;

Figure 3 illustrates another form of cathode ray tube embodying anelectrode system enabling the deflection of the cathode ray immediatelynear the cathode, resulting in greatly increased sensitivity of thereflection;

Figure 4 illustrates a bottom view of the tube according to Figure 3 andthe connections to the deflecting plates from a controlling source;

Figure 5 is a front view of the anode or shielding electrode provided inthe tube shown by Figure 3; and

Figures 6, 6a and 7, 7a schematically illustrate electrode systems forcathode ray tubes employing the shielding element in accordance with myinvention.

In accordance with my invention I provide a means in a cathode ray tubefor accelerating an electron ray from either an initial very lowvelocity or a reduced velocity obtained by previous deceleration to adesired final acceleration without otherwise impairing the operatingcharacteristics and sensitivity of deflection of the electron y.

In accordance with the preferred embodiment of my invention, I havedevised an accelerating electrode insuring a gradual potential variationfrom the place of the initial or starting potential to the finalpotential to which the ray is to be accelerated. According to apreferred construction, I use a tubular shaped unit as an acceleratingelectrode comprising substantially two cylindrical elements providedwith wedge-shaped teeth engaging each other whereby the acceleratingpotential is applied to one of said elements.

This construction is shown in more detail by Figure 1 of the drawing.This illustrates the cylindrical metallic unit, or unit provided with ametal coating, used as an accelerating means in which the cylinder isshown to be cut open lengthwise and spread out into a plane. I haveshown the one element at I 4 provided with wedgeshaped teeth l4 and thesecond cylindrical element at l2 provided with similar wedge-shapedteeth l2 engaging the teeth of the first element as shown. Theembodiment as shown by Figure l is. of a specific and preferred form tobe used for both final acceleration and previous deceleration of theelectron beam, and for this purpose I have shown further wedge-shapedteeth I 4' connected to the other side of the cylindrical element I 4and a further cylindrical element I5 provided with teeth l5 engagingteeth Id of the element M. The arrangement and function of this con-'struction will be explained further in connection with Figure 2.

By providing a suflicient number of teeth in the cylindrical elementsforming the acceleration or deceleration electrodes, the conditionsobtained are such that a highly homogeneous electric field consists forboth undeflected and largely deflected rays passing inside thecylindrical unit.

Generally, the electrode structure for accelerating or decelerating anelectron beam in accordance with the invention is of such configurationand design as to produce an accelerating or decelerating electric fieldwhich exerts a substantially equal force upon the electrons independentof the direction of the beam through the field. In this manner both thedeflected and undeflected beam is accelerated or decelerated in an equalmanner without in any way effecting the characteristics of the beam,such as its initial velocity, degree of concentration, etc. liable toproduce distortion of the pattern or image produced by the beam upon theluminescent screen.

I have furthermore discovered that obviously on account of conditionsprevailing -in the ray generating a concentrating space in gas filledcathode ray tubes and furthermore due to the high stray losses of slowelectron rays even within ranges of only 5 centimeters, it is impossibleto maintain the electron velocity within the deflecting space at verylow values in order to obtain a very high sensitivity of deflection.

I overcome this defect by using a higher initial acceleration voltage inthe ray producing system equal to about one-half to one-eighth of thedesired electron velocity at the luminous screen. I then provide meansfor decelerating the electrons within the deflecting space and in thismanner I have found it possible to secure extremely high degrees ofsensitivity of deflection especially in gas filled cathode ray tubes.The deceleration may be carried out to substantially lower electron voltvelocities as would be possible in the above mentioned case where lowinitial velocity is employed in the space where the ray is produced andinitially concentrated, such as by means of a negatively biasedconcentration cylinder.

When using an initial high electron velocity and subsequentlydecelerating the electrons to a lower velocity in the deflecting space,the deceleration may be carried out by means of ordinary electrodes,such as by the provision of a pair of circular plates with centralopenings for passing the electron ray whereby the braking ordecelerating voltage is applied to the second electrode. However, I havefound that in the case of very high decelerating voltages that the rayis deviated from its central position and deflected more or less in alateral direction so that it is finally prevented from passing throughthe opening of the decelerating electrode.

In accordance with a further feature of the invention, I prevent theaforementioned deviation of the beam by the decelerating field by theprovision of a similar shaped cylindrical electrode system with mutuallyengaging wedge-shaped teeth as hereinbefore described for efiecting afinal or re-acceleration of the electron beam to the desired finalvelocity.

Referring to Figure 2 of the drawing, I have shown a cathode ray tubeembodying an electrode system as described by Figure 1 used for bothdecelerating and subsequently accelerating an electron beam for thepurpose as described. Referring to the drawing, I have illustrated acathode ray tube comprising a glass bulb I having a neck shaped portionhousing the electrode systems for producing and deflecting the electronray and a spherical shaped end portion including an inclined luminousscreen l6 as describedin in? cope'nding application entitledImprovements in and methods of operating cathode ray tubes of even date.Numeral 2 represents a cathode which may be a thermionic filamentarycathode as shown, but it is understood that any other type of cathodemay be provided, such as an indirectly heated cathode of known design inthe art. The cathode is shown to be heated by a battery I and issurrounded by a cylindrical or concentration electrode 3 negativelybiased relative to the cathode by means of a biasing battery as shown at8 for concentrating the electron stream into a sharply focused pencil.At 4 I have shown a positive or anode electrode for producing an initialacceleration of the electron beam emanating from the cathode and theconcentration cylinder 3. The electrode 2 may be of ring-shape with acentral opening and provided with a cylindrical unit having wedge-shapedteeth l5 similar to the unit l5 as described by Figure 1. The electrode2 is connected to a high positive operating potential of about 1000volts such as shown by the battery 9 to initially accelerate theelectron beam. Numeral 10 represents a breaking or decelerationelectrode having a lower positive potential applied to it than theelectrode 2, such as by means of battery II as shown. The electrode l0may also be of circular shape with a central opening for passing theelectron ray and connected to the cylindrical unit M with teeth l4engaging the teeth l5 of element 2 as shown in more detail in Figure 1.In this manner a decelerating electric field is produced within thespace between the electrodes 2 and ID of favorable potentialdistribution to enable the electron ray previously accelerated by theelectrode 2 to be decelerated to a very lowelectron velocity withoutdeviating from the central position, In this manner high sensitivity ofdeflection is obtained, such as by means of the usual deflectingmechanism such as the two pairs of electrostatic deflecting plates 5,and 6, respectively, arranged at right angle to each other as shown inthe drawing.

I 'The'thus deflected electron ray is subsequently reaccelerated to itsfinal velocity by means of the tubular accelerating electrode f2provided with wedge-shaped teeth l2 engaging the teeth I4 of theelectrode Hi. In this manner as pointed out, a re-acceleration of theelectron beameven when deflected to its fullest degree in bothcoordinates isinsured without any substantial impairment of itscharacteristics.

I have shown the accelerating potential which may be of the same valueas the breaking potential (1000 volts in the above example) applied by abattery ISconnected to the element l2. It was furthermore found that theconditions and the operation can be improved by biasing the screen 16 toa potential equal to the accelerating potential such as shown by theconnection of the screen to the plus pole of the battery [3. In theexample as illustrated the potential of the battery ll may be within theorder of 100 volts or less.

In an arrangement for gas filled cathode ray tubes as described, it ispossible to decrease the velocity of the electrons down to almost theionization potential of the gas, especially if the deflecting system isso constructed that the path over which the electrons travel at thelowest velocity through thegas does not exceed two to three centimeters.If still lower voltages are employed, this will result in an impairmentof the definition or Sharpness of the luminescent spot on the screen.Thusflt is preferable to use gases 7 with very low ionization potentialin order to secure very high degrees of sensitivity of deflection as isunderstood. It has furthermore; been found advantageous to use heavygases with the added advantage of increased ray intensity orcorrespondingly decreased losses caused by stray electrons.

While I have described a specific arrangement comprising bothdeceleration and acceleration of the electron ray, it is obvious that Iam not. limited to the specific combination as shown. Thus, it ispossible to use the decelerating mechanism in connection with any otheraccelerating arrangement.

In accordance with a further feature of the invention, it is advisableto provide the electrode Ill with a very small aperture through whichthe low. speed electrons pass, especially in the case of very highdeceleration to very low electron velocities. In some cases I found itadvantageous to cover the opening of the electrode lll with a fine wirenet or grid to secure as straight a course of the lines of field aspossible.

Referring to Figure. 3 of the drawing, I have shown another cathode raytube construction for deflecting the electron beam immediately at thesource or'cathode where theelectron speed is a minimum, thus obtaining amaximum sensitivity of the deflection, as is obvious. This type ofconstruction is especially suited for partly or highly evacuated tubesin which the electron velocity at the cathode may be of a very low valueas compared with gas filled tubes hereinbefore mentioned.

I have shown a special electrode construction mounted at the cathodeserving both for deflecting the electron beam preferably in onedirection and at the same time acting as a means for con.- centratingand focusing the electron stream into a sharp beam together with aspecially construct ed anode electrode, as will be describedhereinafter.

Referring to the drawing Figure 3, Lhave again shown a cathode ray tubecomprising a glass bulb I mounted upon a base ll andprovided with aninwardly projecting press it} for carrying the cathode, anode and thedeflecting system. The cathode ray tube shown in this figure differsfrom Figure 2 by the arrangement of the luminous screen 19 directlyapplied to the inner end wall of the tube in accordance'with well knownconstructions in the art. Numeral 20 represents the cathode similar asdescribed by Figure 2 connected to terminals 20' mounted at the sides ofthe base II. I have furthermore shown a box-like system comprising fourplates 2|, 22, 23 and 24 arranged in square shape close to each otherand surrounding the cathode. Each of the plates'is connected to aconnectingterminal or prong 2|, 22', 23 and 24', respectively, mountedat the bottom of the base H, as shown by Figure 4. Figure 4 also shows across-section of the plate system and the connection to the prongterminals. By the use of an arrangement of this type the electron beamcan be deflected in one direction by applying the controlling potentialsupplied from a transformer or other source [8 shown in Figure 4 to apair of opposite plates, in the example illustrated plates 23 and 24. Inorder to obtain deflection in both directions from the central or zeroposition of v the electron beam, the remaining plates 2! and 22 shouldbe connected to the mid-tap point, of the controlling source H3, in theexample the secondary of the transformer winding as illustrated.

In order to increase the sharpness of the beam which has already beenfocused by the proper choice of the cathode and by the action of theelectrode system II to 24 acting similar to a. concentration cylinder, Ihave found it advisable to provide an anode 25 surrounding the cathodestructure at all sides, such as by means of a circular anode plate 25covering the cylinder 2T surrounding the. entire cathode structure.

In order to insure large deflections of the cathode ray by thedeflecting plate system as shown and preventing the ray from beingobstructed by the anode plate. 2.5, I have shown the latter providedwith a lengthwise slit 25" to allow the beam to sweep over the entiresurface of the luminous screen in a horizontal direction according tothe specific example as shown in more detail by Figure 5. If it isfurther desired to sweep the beam in a vertical direction, a pairofordinary deflecting plates as shown at 26 may be arranged behind theanode 25.

In an arrangement as described, the anode 25 furthermore acts as ascreen between the two deflecting systems for preventing decrease ofsensitivity of the deflection and distortion caused by electrostaticinteraction between the deflecting systems.

It is furthermore understood that a shielding electrode as shown at 25in Figure 3 may be employed in connection with any other electrodesystem in cathode ray tubes and is not limited to the particularconstruction according to Figure 3- in which the shielding electrodesimultaneously acts as an anode for the electron stream.

Thus, referring toFigures 6 and So I have indicated schematically anelectrode system of usual construction in combination with a shieldingelectrode according to the invention. Numeral 28 indicates the cathoderay source such as the concentration cylinder surrounding a cathode.Numeral 29- represents the usual anode which may be in the form of" adisc with a central opening for passing the cathode ray. Numeral 30shows a first pair of deflecting plates to sweep the beam in a verticaldirection. Numeral 3t represents a shielding electrode in accordancewith the invention comprising a disc provided with a vertical slit toallow the beam to sweep vertically between the upper and lowerdeflecting positions, and numeral 32 indicates a second pair ofdeflecting plates for sweeping the beam in a horizontal direction.

Figures 7 and 72 illustrate a similar system with the succession of thedeflectionreversed, in which case the shielding electrode 3 is arrangedwith its slit in a horizontal position, as will be understood.

I claim:

1. The method' of operating cathode ray tubes consisting of producing aconcentrated electron beam; initially accelerating said beam to avelocity being a fraction of the desired final velocity; subsequentlynon-uniformly decelerating said beam to a very low velocity; deflectingsaid beam and re-accelerating the deflected beam for securing a desiredfinal electron velocity.

2. In combination, a cathode ray tube having an envelope; means forproducing a concentrated electron beam therein; means for acceleratingsaid beam to a low velocity; means for deflecting the accelerated beam;means for applying final acceleration tothe deflected beam, said lastvmeans aoson ra comprising a pair of tubular elements provided withwedge-shaped teeth engaging each other in comb fashion and means forapplying electric potential to one of said elements to secure agradually increasing accelerating potentialdistribution from the initialvelocity of said beam to its desired final victory.

3. In combination with a cathode ray tube; means for producing aconcentrated electron beam; means for varying the speed of said beamcomprising a. tubular shaped electrode unit through which the beam ispassed having substantially two elements provided with wedgeshapedmetallic teeth engagingeach other, the open. ends of said units beingcovered with. disc shaped members provided with central openings forpassing the electron beam; and means for applying an electric potentialdifference between said elements.

4.. A cathodev raytube comprising an envelope; means for producing aconcentrated. electron beam therein; a luminous screen for said beamtostrike against; a first substantially discshaped positive acceleratingelectrode to initially accelerate said beam to a predetermined velocity;a second substantially disc shaped decelerating electrode of lowerpositivepotential than said first electrode for decreasing the velocityof said beam to a predetermined value, said second electrode being alsoprovided with a central opening for passing the electron beam, both ofsaid electrodes having tubular extensions mounted thereon withwedge-shaped teeth engaging each other; means for deflecting thed'ecelerated electron beam; and. further means for subsequentlyre-accelerating the deflected beam, said last means consisting of atubular electrode structure comprising substantially two tubularelements provided with wedge-shaped teeth engaging each other with apositive accelerating potential applied to the element closest to saidluminous screen.

5. In a cathode ray tube as claimed in claim 4 in which a combineddecelerating and accelerating electrode structure is provided comprisingtwo outer and one intermediate tubular elements provided. withwedge-shaped teeth engaging each other; means for applying initialaccelerating potential to one of the outer units; means for applyingdecelerating potential to the intermediate unit; and further means forapplying reaccelerating potential to the other outer unit.

6. A cathode ray tube comprising an envelope; a cathode therein; anelectrode structure comprising two pairs of opposite platessymmetrically surrounding said cathode and an anode closely surroundingsaid cathode and said electrode structure whereby the electron streamemitted by said cathode is concentrated into a narrow beam, said anodebeing provided with an opening for passing said electron beam; and meansfor applying deflecting potential to one pair of said plates.

'7. A cathode ray tube comprising an envelope; a cathode therein; anelectrode structure comprised of twopairs of parallel platessymmetrically enclosing said cathode; a cylindrically shaped anodeconcentrically enclosing said cathode and said electrode structurewhereby the electron stream emitted from said cathode is concentratedinto a sharp beam, and a cover mem her for said. anode having a centralopening for passing the said electron beam; and meansfor applyingdeflecting potential difference between one pair of said electrodestructures and a luminescent screen for the electron beam to strikeagainst.

8. In a cathode ray tube as claimed in claim '7 in which said covermember is provided with a lengthwise slit to allow sweeping of said beamover the surface of said luminescent screen.

9. A cathode ray tube comprising an envelope; a thermionic cathodetherein; an electrode structure being comprised of two pairs of parallelmetallic plates arranged at right angle and symmetrically enclosing saidcathode; a substantially symmetrical anode enclosing said cathode andsaid electrode structure whereby the electron stream emitted by saidcathode is concentrated into a beam; a cover member for said anodeprovided with an opening for passing said beam; a source of deflectingpotential being con nected to a pair of said plates enclosing saidcathode; a connection from the remaining pair of plates to the centralpoint of said source; and a luminescent screen for said beam to strikeagainst.

10. In a cathode ray tube as claimed in claim 9 in which said covermember is provided with a lengthwise slit for enabling said beam tosweep over the surface of said screen.

11. In combination, a cathode ray tube having an envelope; means forproducing a concentrated electron beam therein; means for acceleratingsaid beam to a low velocity; means for deflecting said beam; and meansfor applying final acceleration to said deflected beam, said last meanscomprising an electrode structure;

and means for applying an electric potential thereto to secure agradually increasing accelerating potential distribution from the pointof initial velocity to the point of final velocity of the electron beam.

12. The method of operating cathode ray tubes comprising producing aconcentrated electron beam, initially accelerating said beam to a velocity being a fraction of the desired final velocity, subsequentlynon-uniformly decelerating said beam to a very low velocity, deflectingsaid beam and non-uniformly re-accelerating the deflected beam forsecuring a desired final electron velocity.

MANFRED VON ARDENNE.

